This application claims benefit under Title 35, United States Code, xc2xa7119 of Great Britain Patent Application No. 00114286.8, filed on Jun. 12, 2001.
The invention relates to nucleoside derivatives as inhibitors of HCV replicon RNA replication. In particular, the invention is concerned with the use of purine and pyrimidine nucleoside derivatives as inhibitors of subgenomic Hepatitis C Virus (HCV) RNA replication and pharmaceutical compositions containing such compounds.
Hepatitis C virus is the leading cause of chronic liver disease throughout the world. Patients infected with HCV are at risk of developing cirrhosis of the liver and subsequent hepatocellular carcinoma and hence HCV is the major indication for liver transplantation. Only two approved therapies are currently available for, the treatment of HCV infection (R. G. Gish, Sem. Liver. Dis., 1999, 19, 35). These are interferon-xcex1 monotherapy and, more recently, combination therapy of the nucleoside analogue, ribavirin (Virazole), with interferon-xcex1.
Many of the drugs approved for the treatment of viral infections are nucleosides or nucleoside analogues and most of these nucleoside analogue drugs inhibit viral replication, following conversion to the corresponding triphosphates, through inhibition of the viral polymerase enzymes. This conversion to the triphosphate is commonly mediated by cellular kinases and therefore the direct evaluation of nucleosides as inhibitors of HCV replication is only conveniently carried out using a cell-based assay. For HCV the availability of a true cell-based viral replication assay or animal model of infection is lacking.
Hepatitis C virus belongs to the family of Flaviridae. It is an RNA virus, the RNA genome encoding a large polyprotein which after processing produces the necessary replication machinery to ensure synthesis of progeny RNA. It is believed that most of the non-structural proteins encoded by the HCV RNA genome are involved in RNA replication. Lohmann et al. [V. Lohmann et al., Science, 1999, 285, 110-113] have described the construction of a Human Hepatoma (Huh7) cell line in which subgenomic HCV RNA molecules have been introduced and shown to replicate with high efficiency. It is believed that the mechanism of RNA replication in these cell lines is identical to the replication of the full length HCV RNA genome in infected hepatocytes. The subgenomic HCV cDNA clones used for the isolation of these cell lines have formed the basis for the development of a cell-based assay for identifying nucleoside analogue inhibitors of HCV replication.
The invention is concerned with the use of compounds of the formula I 
wherein
R is hydrogen or xe2x80x94[P(O)(OH)xe2x80x94O]nH and n is 1, 2 or 3;
R1 is alkyl, alkenyl, alkynyl, haloalkyl, alkylcarbonyl, alkoxycarbonyl, hydroxyalkyl, alkoxyalkyl, alkoxy, cyano, azido, hydroxyiminomethyl, alkoxyiminomethyl, halogen, alkylcarbonylamino, alkylaminocarbonyl, azidoalkyl or aminomethyl, alkylaminomethyl, dialkylaminomethyl or heterocyclyl;
R2 is hydrogen, hydroxy, amino, alkyl, hydroxyalkyl, alkoxy, halogen, cyano, or azido;
R3 and R4 are hydrogen, hydroxy, alkoxy, halogen or hydroxyalkyl, provided that at least one of R3 and R4 is hydrogen; or
R3 and R4 together represent xe2x95x90CH2 or xe2x95x90Nxe2x80x94OH, or
R3 and R4 both represent fluorine;
X is O, S or CH2;
B signifies a 9-purinyl residue B1 of formula 
wherein
R5 is hydrogen, hydroxy, alkyl, alkoxy, alkylthio, NHR8, halogen or SH;
R6 is hydroxy, NHR8, NHOR9, NHNR8, xe2x80x94NHC(O)OR9xe2x80x2 or SH;
R7 is hydrogen, hydroxy, alkyl, alkoxy, alkylthio, NHR8, halogen, SH or cyano;
R8 is hydrogen, alkyl, hydroxyalkyl arylcarbonyl or alkylcarbonyl;
R9 is hydrogen or alkyl;
R9xe2x80x2 is alkyl; and
B signifies a 1-pyrimidyl residue B2 of formula 
wherein
Z is O or S;
R10 is hydroxy, NHR8, NHOR9, NHNR8, xe2x80x94NHC(O)OR9xe2x80x2 or SH;
R11 is hydrogen, alkyl, hydroxy, hydroxyalkyl, alkoxyalkyl, haloalkyl or halogen;
R8 R9 and R9xe2x80x2 are as defined above;
and of pharmaceutically acceptable salts thereof;
for the treatment of diseases mediated by the Hepatitis C Virus (HCV), pharmaceutical compositions comprising such compounds or for the preparation of medicaments for such treatment.
The compounds of formula I have been shown to be inhibitors of subgenomic Hepatitis C Virus replication in a hepatoma cell line. These compounds have the potential to be efficacious as antiviral drugs for the treatment of HCV infections in human.
In compounds, wherein R is a phosphate group xe2x80x94[P(O)(OH)xe2x80x94O]nH, n is preferably 1. The phosphate group may be in the form of a stabilized monophosphate prodrug or other pharmaceutically acceptable leaving group which when administered in vivo, is capable of providing a compound wherein R is monophosphate. These xe2x80x9cpronucleotidesxe2x80x9d can improve the properties such as activity, bioavailability or stability of the parent nucleotide.
Examples of substituent groups which can replace one or more of the hydrogens in the phosphate moiety are described in C. R. Wagner et al., Medicinal Research Reviews, 2000, 20(6), 417 or in R. Jones and N. Bischofberger, Antiviral Research 1995, 27, 1. Such pronucleotides include alkyl and aryl phosphodiesters, steroid phosphodiesters, alkyl and aryl phosphotriesters, cyclic alkyl phosphotriesters, cyclosaligenyl (CycloSal) phosphotriesters, S-acyl-2-thioethyl (SATE) derivatives, dithioethyl (DTE) derivatives, pivaloyloxymethyl phosphoesters, para-acyloxybenzyl (PAOB) phosphoesters, glycerolipid phosphodiesters, glycosyl lipid phosphotriesters, dinucleosidyl phosphodiesters, dinucleoside phosphotriesters, phosphorodiamidates, cyclic phosphoramidates, phosphoramidate monoesters and phosphoramidate diesters.
The invention also includes pro-drugs or bioprecursors of the parent nucleoside which are converted in vivo to the compound of formula I wherein R is hydrogen, or at least one of R2, R3 and R4 is hydroxy. Preferred pro-drug derivatives include carboxylic esters in which the non-carbonyl moiety of the ester group is selected from straight or branched alkyl (e.g. methyl, n-propyl, n-butyl or tert.-butyl), alkoxyalkyl (e.g. methoxymethyl), aralkyl (e.g. benzyl), aryloxyalkyl (e.g. phenoxymethyl), aryl (e.g. phenyl optionally substituted by halogen, C1-4 alkyl or C1-4 alkoxy or amino); sulphonate esters such as alkylsulphonyl or arylsulphonyl (e.g. methanesulphonyl); amino acid esters (e.g. L-valyl or L-isoleucyl) or pharmaceutically acceptable salts thereof. The preparation is carried out according to known methods in the art, for example methods known from textbooks on organic chemistry (e.g. from J. March (1992), xe2x80x9cAdvanced Organic Chemistry: Reactions, Mechanisms, and Structurexe2x80x9d, 4th ed. John Wiley and Sons).
The term xe2x80x9calkylxe2x80x9d as used herein denotes a straight or branched chain hydrocarbon residue containing 1 to 12 carbon atoms. Preferably, the term xe2x80x9calkylxe2x80x9d denotes a straight or branched chain hydrocarbon residue containing 1 to 7 carbon atoms. Most preferred are methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert.-butyl or pentyl. The alkyl may be unsubstituted or substituted. The substituents are selected from one or more of cycloalkyl, nitro, amino, alkyl amino, dialkyl amino, alkyl carbonyl and cycloalkyl carbonyl.
The term xe2x80x9ccycloalkylxe2x80x9d as used herein denotes an optionally substituted cycloalkyl group containing 3 to 7 carbon atoms, e.g. cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl or cycloheptyl.
The term xe2x80x9calkoxyxe2x80x9d as used herein denotes an optionally substituted straight or branched chain alkyl-oxy group wherein the xe2x80x9calkylxe2x80x9d portion is as defined above such as methoxy, ethoxy, n-propyloxy, i-propyloxy, n-butyloxy, i-butyloxy, tert.-butyloxy, pentyloxy, hexyloxy, heptyloxy including their isomers.
The term xe2x80x9calkoxyalkylxe2x80x9d as used herein denotes an alkoxy group as defined above which is bonded to an alkyl group as defined above. Examples are methoxymethyl, methoxyethyl, methoxypropyl, ethoxymethyl, ethoxyethyl, ethoxypropyl, propyloxypropyl, methoxybutyl, ethoxybutyl, propyloxybutyl, butyloxybutyl, tert.-butyloxybutyl, methoxypentyl, ethoxypentyl, propyloxypentyl including their isomers.
The term xe2x80x9calkenylxe2x80x9d as used herein denotes an unsubstituted or substituted hydrocarbon chain radical having from 2 to 7 carbon atoms, preferably from 2 to 4 carbon atoms, and having one or two olefinic double bonds, preferably one olefinic double bond. Examples are vinyl, 1-propenyl, 2-propenyl (allyl) or 2-butenyl (crotyl).
The term xe2x80x9calkynylxe2x80x9d as used herein denotes to unsubstituted or substituted hydrocarbon chain radical having from 2 to 7 carbon atoms, preferably 2 to 4 carbon atoms, and having one or where possible two triple bonds, preferably one triple bond. Examples are ethynyl, 1-propynyl, 2-propynyl, 1-butynyl, 2-butynyl or 3-butynyl.
The term xe2x80x9chydroxyalkylxe2x80x9d as used herein denotes a straight or branched chain alkyl group as defined above wherein 1, 2, 3 or more hydrogen atoms are substituted by a hydroxy group. Examples are hydroxymethyl, 1-hydroxyethyl, 2-hydroxyethyl, 1-hydroxypropyl, 2-hydroxypropyl, 3-hydroxypropyl, hydroxyisopropyl, hydroxybutyl and the like.
The term xe2x80x9chaloalkylxe2x80x9d as used herein denotes a straight or branched chain alkyl group as defined above wherein 1, 2, 3 or more hydrogen atoms are substituted by a halogen. Examples are 1-fluoromethyl, 1-chloromethyl, 1-bromomethyl, 1-iodomethyl, trifluoromethyl, trichloromethyl, tribromomethyl, triiodomethyl, 1-fluoroethyl, 1-chloroethyl, 1-bromoethyl, 1-iodoethyl, 2-fluoroethyl, 2-chloroethyl, 2-bromoethyl, 2-iodoethyl, 2,2-dichloroethyl, 3-bromopropyl or 2,2,2-trifluoroethyl and the like.
The term xe2x80x9calkylthioxe2x80x9d as used herein denotes a straight or branched chain (alkyl)Sxe2x80x94 group wherein the xe2x80x9calkylxe2x80x9d portion is as defined above. Examples are methylthio, ethylthio, n-propylthio, i-propylthio, n-butylthio, i-butylthio or tert.-butylthio.
The term xe2x80x9carylxe2x80x9d as used herein denotes an optionally substituted phenyl and naphthyl (e.g. 1-naphthyl, 2-naphthyl or 3-naphthyl). Suitable substituents for aryl can be selected from those named for alkyl, in addition however, halogen, hydroxy and optionally substituted alkyl, haloalkyl, alkenyl, alkynyl and aryloxy are substituents which can be added to the selection.
The term xe2x80x9cheterocyclylxe2x80x9d as used herein denotes an optionally substituted saturated, partially unsaturated or aromatic monocyclic, bicyclic or tricyclic heterocyclic systems which contain one or more hetero atoms selected from nitrogen, oxygen and sulfur which can also be fused to an optionally substituted saturated, partially unsaturated or aromatic monocyclic carbocycle or heterocycle.
Examples of suitable heterocycles are oxazolyl, isoxazolyl, furyl, tetrahydrofuryl, 1,3-dioxolanyl, dihydropyranyl, 2-thienyl, 3-thienyl, pyrazinyl, isothiazolyl, dihydrooxazolyl, pyrimidinyl, tetrazolyl, 1-pyrrolidinyl, 2-pyrrolidinyl, 3-pyrrolidinyl, pyrrolidinonyl, (N-oxide)-pyridinyl, 1-pyrrolyl, 2-pyrrolyl, triazolyl e.g. 1,2,3-triazolyl or 1,2,4-triazolyl, 1-pyrazolyl, 2-pyrazolyl, 4-pyrazolyl, piperidinyl, morpholinyl (e.g. 4-morpholinyl), thiomorpholinyl (e.g. 4-thiomorpholinyl), thiazolyl, pyridinyl, dihydrothiazolyl, imidazolidinyl, pyrazolinyl, piperazinyl, 1-imidazolyl, 2-imidazolyl, 4-imidazolyl, thiadiazolyl e.g. 1,2,3-thiadiazolyl, 4-methylpiperazinyl, 4-hydroxypiperidin-1-yl.
Suitable substituents for heterocyclyl can be selected from those named for alkyl, in addition however, optionally substituted alkyl, alkenyl, alkynyl, an oxo group (xe2x95x90O) or aminosulphonyl are substituents which can be added to the selection.
The term xe2x80x9cacylxe2x80x9d (xe2x80x9calkylcarbonylxe2x80x9d)as used herein denotes a group of formula C(xe2x95x90O)R wherein R is hydrogen, an unsubstituted or substituted straight or branched chain hydrocarbon residue containing 1 to 7 carbon atoms or a phenyl group. Most preferred acyl groups are those wherein R is hydrogen, an unsubstituted straight chain or branched hydrocarbon residue containing 1 to 4 carbon atoms or a phenyl group.
The term halogen stands for fluorine, chlorine, bromine or iodine, preferable fluorine, chlorine, bromine.
Within the invention the term xe2x80x9cXxe2x80x9d represents O, S or CH2, preferably O or CH2. Most preferred xe2x80x9cXxe2x80x9d represents O.
Within the invention the term xe2x80x9cZxe2x80x9d represents O or S, preferably O.
In the pictorial representation of the compounds given throughout this application, a thickened tapered line () indicates a substituent which is above the plane of the ring to which the asymmetric carbon belongs and a dotted line () indicates a substituent which is below the plane of the ring to which the asymmetric carbon belongs.
Compounds of formula I exhibit stereoisomerism. These compounds can be any isomer of the compound of formula I or mixtures of these isomers. The compounds and intermediates of the present invention having one or more asymmetric carbon atoms may be obtained as racemic mixtures of stereoisomers which can be resolved.
Compounds of formula I exhibit tautomerism that means that the compounds of this invention can exist as two or more chemical compounds that are capable of facile interconversion. In many cases it merely means the exchange of a hydrogen atom between two other atoms, to either of which it forms a covalent bond. Tautomeric compounds exist in a mobile equilibrium with each other, so that attempts to prepare the separate substances usually result in the formation of a mixture that shows all the chemical and physical properties to be expected on the basis of the structures of the components.
The most common type of tautomerism is that involving carbonyl, or keto, compounds and unsaturated hydroxyl compounds, or enols. The structural change is the shift of a hydrogen atom between atoms of carbon and oxygen, with the rearrangement of bonds. For example, in many aliphatic aldehydes and ketones, such as acetaldehyde, the keto form is the predominant one; in phenols, the enol form is the major component.
Compounds of formula I which are basic can form pharmaceutically acceptable salts with inorganic acids such as hydrohalic acids (e.g. hydrochloric acid and hydrobromic acid), sulphuric acid, nitric acid and phosphoric acid, and the like, and with organic acids (e.g. with acetic acid, tartaric acid, succinic acid, fumaric acid, maleic acid, malic acid, salicylic acid, citric acid, methanesulphonic acid and p-toluene sulphonic acid, and the like). The formation and isolation of such salts can be carried out according to methods known in the art.
Preferred is the use of compounds of formula I, wherein
R is hydrogen;
R1 is alkyl, alkenyl, alkynyl, haloalkyl, alkylcarbonyl, alkoxy, hydroxymethyl, cyano, azido, alkoxyiminomethyl, alkylcarbonylamino, alkylaminomethyl or dialkylaminomethyl;
R2 is hydrogen, hydroxy, alkoxy or halogen;
R3 and R4 are hydrogen, hydroxy, alkoxy, halogen or hydroxyalkyl, provided that at least one of R3 and R4 is hydrogen; or
R3 and R4 represent fluorine;
X is O or CH2; and
B signifies a 9-purinyl residue B1 or a 1-pyrimidyl residue B2 as defined above.
Examples of preferred compounds are listed below
An especially preferred group of compounds for the treatment of HCV are those of formula I-a 
wherein
R1 is alkyl, alkenyl, alkynyl, haloalkyl, alkylcarbonyl, alkoxy, hydroxymethyl, cyano, azido, alkoxyiminomethyl, alkylcarbonylamino, alkylaminomethyl or dialkylaminomethyl;
R2 is hydrogen, hydroxy, alkoxy, or halogen;
R3 and R4 are hydrogen, hydroxy, alkoxy, halogen or hydroxyalkyl, provided that at least one of R3 and R4 is hydrogen; or
R3 and R4 represent fluorine.
and pharmaceutically acceptable salts.
Examples of such especially preferred compounds are listed below
Most preferred compounds for the treatment of HCV are listed below:
The compounds of formula I may be prepared by various methods known in the art of organic chemistry in general and nucleoside analogue synthesis in particular. The starting materials for the syntheses are either readily available from commercial sources or are known or may themselves be prepared by techniques known in the art. General reviews of the preparation of nucleoside analogues are included in the following publications:
A M Michelson xe2x80x9cThe Chemistry of Nucleosides and Nucleotidesxe2x80x9d, Academic Press, New York 1963.
L Goodman xe2x80x9cBasic Principles in Nucleic Acid Chemistryxe2x80x9d Ed P O P Ts""O, Academic Press, New York 1974, Vol. 1, chapter 2.
xe2x80x9cSynthetic Procedures in Nucleic acid Chemistryxe2x80x9d Ed W W Zorbach and R S Tipson, Wiley, New York, 1973, Vol. 1 and 2.
The synthesis of carbocylic nucleosides has been reviewed by L Agrofoglio et al, Tetrahedron, 1994, 50, 10611.
The strategies available for the synthesis of compounds of formula I include:
1. modification or interconversion of performed nucleosides; or
2. construction of the heterocyclic base after glycosylation; or
3. condensation of a protected furanose, thiofuranose or cyclopentane derivative with a pyrimidine (B2) or purine (B1) base.
These methods will be further discussed below:
1. Modification or Inter-conversion of Preformed Nucleosides
Such methods include on the one hand modification of the 9-purinyl or 1-pyrimidyl residue or on the other hand modification of the carbohydrate moiety.
A. Modification of the Purinyl or Pyrimidyl Moiety
a) The deamination of aminopurine or aminopyrimidine nucleosides as described by J. R. Tittensor and R. T. Walker European Polymer J., 1968, 4, 39 and H. Hayatsu, Progress in Nucleic Acid Research and Molecular Biology 1976, Vol. 16, p75.
b) The conversion of the 4-hydroxy group of 4-hydroxypyrimidine nucleosides to a leaving group and displacement with nucleophilic reagents. Such leaving groups include halogen as described by J. Brokes and J. Beranek, Col. Czech. Chem. Comm., 1974, 39, 3100 or 1,2,4-triazole as described by K. J. Divakar and C. B. Reece, J. Chem. Soc. Perkin Trans. 1, 1982, 1171.
c) 5-Substitution of pyrimidine nucleosides has been achieved by the use of 5-metallo derivatives such as 5-mercuri or 5-palladium for example as described by D. E. Bergstrom and J. L. Ruth J. Amer. Chem. Soc., 1976, 98, 1587. Introduction of fluoro into the 5 position of pyrimidine nucleosides can be achieved with reagents such as trifluoromethyl hypofluorite as described by M. J. Robins, Ann New York Acad. Sci. 1975, 255, 104.
d) Modified purine nucleosides may be prepared from the corresponding purine nucleoside derivatives wherein the 2, 6 or 8 substituent is a suitable leaving group such as halogen or sulphonate or 1,3,4-triazole. 6 substituted purine nucleosides may be prepared by treatment of the appropriate 6-halopurine or 6-(1,2,4-triazol-4-yl)-purine nucleoside derivatives with the appropriate nucleophilic reagent as described by V. Nair and A. J. Fassbender Tetrahedron, 1993, 49, 2169 and by V. Samano, R. W. Miles and M. J. Robins, J. Am. Chem. Soc., 1994, 116, 9331. Similarly 8-substituted purine nucleosides can be prepared by treatment of the corresponding 8-halopurine nucleoside with the appropriate nucleophilic reagent as described by L. Tai-Shun, C. Jia-Chong, I. Kimiko and A. C. Sartorelli, J. Med. Chem., 1985, 28, 1481; Nandanan et al, J. Med. Chem., 1999, 42, 1625; J. Jansons, Y. Maurinsh, and M. Lidaks, Nucleosides Nucleotides, 1995, 14, 1709. Introduction of an 8-cyano substituent can be accomplished by displacement using a metal cyanide as described by L-L. Gundersen, Acta. Chem. Scand. 1996, 50, 58. 2-Modified purine nucleoside may be prepared in a similar fashion as described by T. Steinbrecher, C. Wamelung, F. Oesch and A. Seidl, Angew. Chem. Int. Ed. Engl., 1993, 32, 404.
e) Where the substituent at the 2 or 8-position of the purine nucleoside is linked via a carbon carbon bond e.g. alkyl, then metal catalysed cross-coupling procedures can be used starting with the appropriate 2 or 8-halosubstituted purine nucleoside analogue as described by A. A. Van Aerschott, et al, J. Med. Chem., 1993, 36, 2938; V. Nair and G. S. Buenger, J.Am.Chem.Soc., 1989, 111(22), 8502; C. Tu, C. Keane and B. E. Eaton Nucleosides Nucleotides, 1995, 14, 1631.
B. Modification of the Carbohydrate Moiety
Following introduction of protecting groups which are compatible with the further chemistry:
Azide may be introduced at the 4xe2x80x2-position by treatment of the 4xe2x80x2,5xe2x80x2-didehydro nucleoside with iodine azide as exemplified by H. Maag et al, J. Med. Chem., 1992, 35, 1440. An alkoxide may be introduced at the 4xe2x80x2-position by treatment of the 4xe2x80x2,5xe2x80x2-didehydro nucleoside with iodine followed by an alcohol and lead carbonate as exemplified by J. P. Verheyden and J. G. Moffatt, J.Am.Chem.Soc., 1975, 97(15), 4386. Fluoride maybe introduced at the 4xe2x80x2-position by treatment of the 4xe2x80x2,5xe2x80x2-didehydro nucleoside with iodine followed by silver(I)fluoride as described by G. R. Owen et al, J.Org.Chem., 1976, 41(8), 3010 or A. Maguire et al, J. Chem. Soc. Perkin Trans. 1, 1993, 1(15), 1795. A 4xe2x80x2-formyl group can be introduced and subsequently converted to a wide range of substituents including but not limited to 4xe2x80x2-haloalkyl, 4xe2x80x2-ethynyl, 4xe2x80x2-oximinomethyl, and 4xe2x80x2-cyano as exemplified by M. Nomura et al., J. Med. Chem., 1999, 42, 2901.
Modification of either the 2xe2x80x2-hydroxy substituent or 3xe2x80x2-hydroxy substituent in the nucleoside analogue is possible.
Conversion of the 3- hydroxy to a leaving group such as halo by reaction with for example triphenyl phosphine and a tetrahaloalkane as described for example by L. De Napoli et al, Nucleosides Nucleotides, 1993, 12, 981, followed by reduction provides the 3-deoxysugar derivatives as described by D. G. Norman and C. B. Reese, Synthesis 1983, 304.
Derivatisation of the 3 hydroxy group by conversion to a triflate group followed by reduction using sodium borohydride as described by S. A. Surzhykov et al, Nucleosides Nucleotides, 1994, 13(10), 2283. Direct introduction of a fluorine substituent can be accomplished with fluorinating agents such as diethylaminosulphur trifluoride as described by P. Herdewijn, A. Van Aerschot and L. Kerremans, NucleosidesNucleotides, 1989,8, 65.
Conversion of the hydroxy substituent to a leaving group such as halo or sulphonate also allows displacement using nucleophilic reagents such as tetrabutylammonium fluoride, lithium azide, or metal cyanides as exemplified by H. Hrebabecky, A. Holy and E. de Clercq, Collect. Czech. Chem. Comm. 1990, 55, 1800; K. E. B. Parkes and K. Taylor, Tet. Lett., 1988, 29, 2995; H. M. Pfundheller et al, Helv. Chim. Acta, 2000, 83, 128.
Reaction of 2xe2x80x2-keto nucleosides with fluorinating agents such as diethylamino sulfur trifluoride can be used to prepare 2xe2x80x2,2xe2x80x2-difluoronucleosides as described by D. Bergstrom, E. Romo and P. Shum Nucleosides Nucleotides, 1987, 6, 53.
2. Construction of the Heterocyclic Base after Glycosylation
a) those which for example utilise furanosylamine derivatives as described by N. J. Cusack, B. J. Hildick, D. H. Robinson, P. W. Rugg and G. Shaw J. Chem. Soc. Perkin Trans., I 1973, 1720 or G. Shaw, R. N. Warrener, M. H. Maguire and R. K. Ralph, J. Chem. Soc., 1958, 2294.
b) those which utilise for example furanosylureas for pyrimidine nucleoside synthesis as described by J. {haeck over (S)}mejkal, J. Farkas, and F. {haeck over (S)}orm, Coll. Czech. Chem. Comm., 1966, 31, 291.
c) the preparation of purine nucleosides from imidazole nucleosides is reviewed by L. B. Townsend, Chem. Rev., 1967, 67, 533.
d) the preparation of compounds of formula I wherein X is CH2 can be accomplished from 1-hydroxymethyl-4-aminocyclopentane derivatives as described by Y. F. Shealy and J. D. Clayton J. Am. Chem. Soc., 1969, 91, 3075; R. Vince and S. Daluge J. Org. Chem., 1980, 45, 531; R. C. Cermak and R. Vince, Tet. Lett., 1981, 2331; R. D. Elliott et al, J. Med. Chem., 1994,37, 739.
3. Condensation of a Protected Furanose, Thiofuranose or Cyclopentane Derivative with a Purine or Pyrimidine Derivative
The condensation reaction of a protected furanose, thiofuranose or cyclopentane derivative with an appropriate purine or pyrimidine derivative may be performed using standard methods including the use of a Lewis acid catalyst such as mercuric bromide or stannic chloride or trimethylsilyltrifluoromethane sulphonate in solvents such as acetonitrile, 1,2-dichloroethane, dichloromethane, chloroform or toluene at reduced, ambient or elevated temperature. Examples for the condensation reaction of a protected furanose or thiofuranose
with heavy metal derivatives of purines or pyrimidines derivatives (e.g. chloromercuri derivatives) are described by J Davoll and B. A. Lowry, J. Am. Chem. Soc., 1951, 73, 1650; J. J. Fox, N. Yung, J. Davoll and G. B. Brown, J. Am. Chem. Soc., 1956, 78, 2117.
with alkoxy pyrimidines are described by K. A. Watanabe, D. H. Hollenberg and J. J. Fox., Carbohydrates. Nucleosides and Nucleotides. 1974, 1,1.
with silyl derivatives of purines or pyrimidines as described by U. Niedballa and H. Vorbruggen, J. Org. Chem., 1976, 41, 2084; U. Niedballa and H. Vorbruggen, J. Org. Chem., 1974, 39, 3672. A. J. Hubbard, A. S. Jones and R. T. Walker, Nucleic Acids Res., 1984, 12, 6827.
Furthermore
the fusion of per-acylated sugars with purines under vacuum in the presence of p-toluene sulphonic acid has been described by T. Simadate, Y. Ishudo and T. Sato, Chem. Abs., 1962, 56, 11 692 and W. Pfleiderer, R. K. Robins, Chem. Ber. 1965, 98, 1511.
the condensation reactions have been described by K. A. Watanabe, D. H. Hollenberg and J. J. Fox, Carbohydrates Nucleosides and Nucleotides, 1974, 1,1.
Examples for the condensation reaction of a protected cyclopentane derivative with an appropriate purine derivative or pyrimidine derivative are given in H. Kapeller, H. Baumgartner and H. Griengl, Monattsh Chem., 1997, 128, 191 and P. Wang et al, Tet. Lett., 1997, 38,4207; or by T. Jenny et al. Helv. Chim. Acta, 1992, 25, 1944.
Such methods often result in mixtures of anomeric nucleoside derivatives which can be separated by standard techniques known to the art such as recrystallisation, column chromatography, high performance liquid chromatography or super critical fluid chromatography.
The purine derivatives and pyrimidines derivatives for above condensation reactions can be obtained commercially or can be prepared by procedures known to the art.
The preparation of purine derivatives is reviewed by G. Shaw in xe2x80x9cComprehensive Heterocyclic Chemistryxe2x80x9d pub Pergamon Press Vol. 5 chapter 4. 09, p 499 and xe2x80x9cComprehensive Heterocyclic Chemistry IIxe2x80x9d publ. Pergamon Press, Vol 7, chapter 7. 11, p 397.
The preparation of pyrimidines derivatives is reviewed by D. J. Brown in xe2x80x9cThe Chemistry of Heterocyclic Compoundsxe2x80x94The Pyrimidinesxe2x80x9d 1962 and Supplement 1, 1970, pub John Wiley and Sons, New York, by D. J. Brown in xe2x80x9cComprehensive Heterocyclic Chemistryxe2x80x9d pub Pergamon Press Vol. 5 chapter 4. 09, p 499 and by K. Unheim and T. Benneche in xe2x80x9cComprehensive Heterocyclic Chemistry IIxe2x80x9d pub Pergamon Press Vol. 6 chapter 6. 02 p 93.
Furanose derivatives can be prepared from commercially available carbohydrate starting materials such as the D forms of ribose, arabinose, xylose or lyxose, following introduction of protecting groups which are compatible with the chemistry.
4-Substituted furanoses with the substituent containing a carbon attached to the 4-position of the furanose, for example alkyl, alkenyl, alkynyl, haloalkyl, acyl, alkoxycarbonyl, hydroxyalkyl, alkoxyalkyl, cyano, oximinomethyl, alkoxyiminomethyl, alkylaminocarbonyl and acyl can be prepared from the corresponding 4-formyl furanose. The preparation of one such 4-formylfuranose is described by H. Ohrui et al., J. Med. Chem., 2000, 43, 5416. 4-Haloalkyl furanoses may be prepared from the corresponding 4-hydroxymethyl furanoses (e.g., K. Kitano et al, Tetrahedron, 1997, 53(39), 13315). 4-Methyl furanoses can be prepared by the method described by T. Waga et al, Biosci. Biotech. Biochem. 1993, 19(7), 408.
2,2-Difluorofuranose derivatives can be prepared from D-glucose or D-mannose as described by R. Fernandez, M. I. Mateu, R. Echarri and S. Castillon Tetrahedron, 1998, 54, 3523. The thiofuranose derivatives can be prepared by literature procedures such as L. Bellon, J. L. Barascut, J. L. Imbach, Nucleosides and Nucleotides 1992, 11, 1467 and modified in a similar fashion to the furanose analogues described above.
The cyclopentane derivatives can be prepared by methods known in the art of organic chemistry and by methods and references included in L. Agrofolio et al, Tetrahedron, 1994, 50, 10611.
The preformed nucleoside derivatives are either available commercially or synthesised in accordance with the methods described above.
The methods discussed above are described in more details below:
The compounds of formula I, wherein R1 is N3, R2 and R3 are hydroxy and B is B2 can be prepared according to Reaction Scheme A: 
wherein Ac is acetyl, Bz is benzoyl and R11 is as defined above.
Compounds of Formula II may be iodinated using a mixture of triphenylphosphine, iodine and pyridine as exemplified by H. Maag et al, J. Med. Chem., 1992, 35, 1440. The acetonide protecting group can be removed by treatment with an acid, for instance acetic acid, as described by J. P. Verheyden et al, J. Org. Chem., 1970, 35(7), 2319, to give nucleosides of formula III. Following protection of the 2xe2x80x2 and 3xe2x80x2 hydroxyls with acetic anhydride and pyridine elimination of hydrogen iodide, with for example silver fluoride in pyridine and removal of the acetyl protecting groups with methanolic ammonia as described by J. P. Verheyden et al., J. Org. Chem., 1974, 39(24), 3573, gives 4xe2x80x2,5xe2x80x2 didehydro nucleosides of formula V. Addition of iodine azide to the double bond can be accomplished by treatment of V with a mixture of iodine chloride and sodium azide in N,N-dimethylformamide as described by H. Maag et al, J. Med. Chem., 1992, 35, 1440, to give nucleosides of formula VI. Protection of the hydroxy groups in VI can be accomplished by treatment of VI with benzoyl chloride in pyridine, giving nucleosides of formula VII, which can then be converted into the 5xe2x80x2-benzoyl nucleosides of formula VIII by treatment with meta-chloroperbenzoic acid in dichloromethane, which can then be deprotected with a base, eg sodium methoxide, in methanol to give nucleosides of formula IX, all as described by H. Maag et al, J. Med. Chem., 1992, 35, 1440. In the case where B2 in the compound of formula VIII is uracil or 5xe2x80x2-substituted uracil, following protection of the 3xe2x80x2-hydroxy group with acetic anhydride and pyridine, conversion to the corresponding cytidine of formula XII can be accomplished by the method described by A. D. Borthwick et al., J. Med. Chem., 1990, 33(1), 179, whereby nucleosides of formula X can be treated with 4-chlorophenyl dichlorophosphate and triazole to give 4-triazolyl nucleosides of formula XI, followed by treatment of nucleosides XI with aqueous ammonia giving 5-substituted cytidines of formula XII.
Compounds of formula I, wherein R1 is xe2x80x94Cxe2x89xa1CH, xe2x80x94CHxe2x95x90CHCl, xe2x80x94CHxe2x95x90Nxe2x80x94OH, xe2x80x94CN, R2 and R3 are hydroxy and B is B1 or B2 can be prepared according to Reaction Scheme B. 
Compounds of formula XIII can be silylated with tert-butyldimethylsilylchloride (TBSCl) and imidazole to give the tri-tert-butyldimethylsilyl compounds of formula XIV. The 5xe2x80x2-tert-butyldimethylsilyl ether can be deprotected using 80% acetic acid to give the 5-hydroxy nucleosides XV, which can then be oxidised to the 5xe2x80x2-formyl nucleosides XVI using a mixture of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDAC) and dimethyl-sulphoxide (DMSO) in a suitable solvent, eg benzene. Alkylation of XVI with formaldehyde and sodium hydroxide gives the 4xe2x80x2-hydroxymethyl compounds XVII which can be reduced to the 4xe2x80x2-dihydroxymethyl compounds XVIII. Selective protection of the hydroxymethyl on the xcex1 face of the nucleoside with trityl chloride in pyridine gives the 4xe2x80x2-trityl compounds XIX, followed by protection of the hydroxymethyl on the xcex2-face of the nucleoside with tert-butyldimethyl-silylchloride (TBSCl) and imidazole gives compounds of formula XX. Deprotection of the trityl group with bromocatecholborane gives the 4xe2x80x2-hydroxymethyl compound XXI, which can be oxidised with trifluoromethanesulphonic anhydride and dimethylsulphoxide to give the 4xe2x80x2-formyl compound of formula XXII.
The aldehyde of formula XXII can be used as starting material for a wide range of 4xe2x80x2-substituted nucleosides as depicted in Scheme C: 
Treatment of the aldehyde XXII with hydroxylamine hydrochloride and pyridine gives the 4xe2x80x2-hydroxyimine of formula XXIII. Water is eliminated from compound XXIII to give 4xe2x80x2-cyano compounds of formula XXIV. Treatment of 4xe2x80x2-formyl compounds of formula XXII with chloromethylphosphonium chloride and butyl lithium gives the 4xe2x80x2-(2-chloroethenyl) compounds XXVI. Treatment of compounds XXVI with butyllithium results in the elimination of hydrogen chloride to give the 4xe2x80x2-ethynyl compounds of formula XXVII. Removal of the silyl protecting groups from the tri tert-butyldimethylsilylchloride protected compounds XXIII, XXVII and XXIV can be carried out with a fluoride source such as ammonium fluoride in methanol or tetrabutylammonium fluoride absorbed on silica in tetrahydrofuran, to give the respective 4xe2x80x2-substituted nucleosides XXV, XXVIII and XXIX.
Suitably protected 4xe2x80x2-substituted uridines (for example XXIV and XXVII) can be converted to the corresponding 4xe2x80x2-substituted cytidines according to Reaction Scheme D. 
The tri-tertbutyldimethylsilyl (TBS) protected uridines of formula XXX can be treated with tri-isopropylbenzenesulphonyl chloride, triethylamine and dimethylaminopyridine to give the 4-triazolylnucleosides XXXI. The 4-triazolyl compounds XXXI can be converted to the 4-amino compounds XXXII with aqueous ammonia. Deprotection of the silyl groups with a mixture of methanol and hydrochloric acid in dioxan gives the cytidine derivatives XXXIII.
Compounds of formula I, wherein R1 is alkoxy, R2 and R3 are hydroxy and B is a 9-purinyl residue B1 or a 1-pyrimidyl residue B2 can be prepared according to the procedures described by J. P. Verheyden et al. U.S. Pat. No. 3,910,885
Compounds of formula I in which R1 is trifluoromethyl, methyl or ethynyl can be prepared as depicted in Reaction Scheme E: 
for example by coupling the appropriate protected 4xe2x80x2-substituted ribofuranoside XXXIV with a silylated base in the presence of a Lewis acid, eg
trimethylsilyltrifluoromethanesulphonate (TMSOTf) or tin tetrachloride, in an appropriate solvent, eg acetonitrile or 1,2-dichloroethane, to give compound of formula XXXV. The protecting groups can be removed by treatment of XXXV with a base, for example sodium methoxide, in compatible solvent for instance methanol to give compounds of formula XXXVI.
Methods for the monophosphorylation of organic compounds including nucleosides have been reviewed by L A Slotin, Synthesis, 1977, 737. More recently other nucleoside phosphorylation procedures have been described: M Uchiyama et al J. Org. Chem., 1993, 58,373; R Caputo et al, Synlett., 1997, 739 and M Taktakishvili and V Nair Tet. Lett. 2000, 41, 7173. Other procedures for monophosphorylation that may be useful for nucleosides are described by C E McKenna and J Schmidhauser, J.Chem.Soc.,Chem.Commun., 1979, 739 and J K Stowell and T S Widlanski Tet. Lett., 1995, 1825. Synthesis of di and triphosphate derivatives are reviewed in K H Scheit, Nucleotide Analogues, 1980, Wiley Interscience and by K Burgess and D Cook Chemical Reviews, 2000, 100, 2047.